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A telomere (/ ˈ t ɛ l ə m ɪər, ˈ t iː l ə-/; from Ancient Greek τέλος (télos) 'end' and μέρος (méros) 'part') is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes (see Sequences). Telomeres are a widespread genetic feature most commonly found in eukaryotes.
When the cell does this due to telomere-shortening, the ends of different chromosomes can be attached to each other. This solves the problem of lacking telomeres, but during cell division anaphase, the fused chromosomes are randomly ripped apart, causing many mutations and chromosomal abnormalities. As this process continues, the cell's genome ...
Telomerase RNA component, also known as TR, TER or TERC, is an ncRNA found in eukaryotes that is a component of telomerase, the enzyme used to extend telomeres. [3] [4] TERC serves as a template for telomere replication (reverse transcription) by telomerase.
Shelterin (also called telosome) is a protein complex known to protect telomeres in many eukaryotes from DNA repair mechanisms, as well as to regulate telomerase activity. In mammals and other vertebrates, telomeric DNA consists of repeating double-stranded 5'-TTAGGG-3' (G-strand) sequences (2-15 kilobases in humans) along with the 3'-AATCCC-5' (C-strand) complement, ending with a 50-400 ...
As telomeres do not contain a canonical stop codon signaling the end of RNA transcription, it remains unclear exactly where transcription ceases along the telomere tracks. Similarly to most mRNAs transcribed in the nucleus, nearly all TERRA transcripts contain a 7-methylguanosine (m 7 G) cap structure at their 5' end. [10]
The end replication problem is handled in eukaryotic cells by telomere regions and telomerase. Telomeres extend the 3' end of the parental chromosome beyond the 5' end of the daughter strand. This single-stranded DNA structure can act as an origin of replication that recruits telomerase.
The direct visualization of G-quadruplex structures in human cells [47] as well as the co-crystal structure of an RNA helicase bound to a G-quadruplex [48] have provided important confirmations of their relevance to cell biology. The potential positive and negative roles of quadruplexes in telomere replication and function remains controversial.
Sgo2 remains in subtelomeres, whose cells lack telomere DNA. Sgo2 represses the expression of subtelomeric genes that is in a different pass-way from the H3K9me3- Swi6-mediated heterochromatin. Sgo2 has also repressive effects for timing of subtelomeres replication by suppressing Sld3, [25] a replication factor, at the start of the replication ...